What is gear backlash and how is it controlled?

Backlash is the clearance between mating gear teeth when they are in mesh, necessary to prevent jamming due to thermal expansion and manufacturing tolerances. Excessive backlash causes noise, vibration, and positional inaccuracy. It is controlled by tighter manufacturing tolerances (AGMA quality class), center distance adjustment, spring-loaded split gears, or anti-backlash gear mechanisms. For precision applications like CNC machines, backlash should be less than 0.04mm. Zero backlash is achieved using preloaded duplex gears.